This
is the plan of a kiln with a bourry
firebox.At
the suggested scale it is easily built using standard 9ins x 4.5ins x
3ins bricks, and easily fired. If made with dense firebricks it would
be good for salting. More diagrams and comments will be added later.
The flashy colors are not just for show as some of these areas need
to be identified. The plan can be modified provided certain
proportions are maintained. The diagrams below are based on the plan
set out by Janine King and Steve Harrison in their useful booklet
Layed Back Wood Firing,
the third
edition of which is now
available . Photos of a similar kiln being built can be seen here(external
link).

Stoking
is done through the area covered by the firebox lid. The firebox
door is used in the initial stages of firing while the fire is
very small. It is also necessary for cleaning out ash and for
maintaining the mousehole system.

The
mousehole has to be protected by some sort of structure to avoid
clogging and to distribute the air into the bed of embers.

The
number and total area of the exit flues (fig 5) are significant
and must be kept in proportion to the other critical areas if the
plan is modified.

To
make sensible use of these figures it should be kept in mind that the
part of the kiln where the pots are stacked should be approximately in
the shape of a cube.

In
practice, the throat arch area is easily diminished by a build-up
of embers with some woods, and in small kilns it could be made
proportionally larger. Link here
to
see a small double bourry box kiln where I have successfully used
the ratios
A = 7.6, B = 7, C = 14.2, D = 56.5 and V = 11.7% of
W

Figure
6 shows how the chimney is tapered above the exit flues. The
damper can be made from an old kiln shelf. A sheet of metal will
do but will tend to warp and get stuck in position.